The carburetors utilized for handheld chain saws and similar tools have an idle-nozzle system and a main nozzle system. These two nozzle systems are both charged with fuel from a membrane chamber and have a certain functional relationship and each influences the other at least in part. A one-way valve is provided in the main nozzle and is configured as a check valve. It is a disadvantage that this one-way valve does not close without difficulty during no-load operations, for example, because of oscillations in the chain saw so that undesired drops of fuel can leak out. The idle system is thereby disturbed by the main nozzle system. Since for operation under load, the idle system continues to operate in parallel to the main nozzle system, a further influence can occur so that no precise terminal rotational speed and optimal effective efficiency for full load can be guaranteed.